1. Basics

library(structr)

Import

From a Strabospot project, download the json file and import it using the read_strabo_JSON() function.

This returns a list which contains all the information and metadata (including coordinates, descriptions etc) extracted from the Strabospot project in the list element data, the tags used for the project in the list element tags, and the linear and planar orientation measurements in the list elements lines and planes, respectively.

Data conversion to spherical objects

Usually orientation data is stored in a table containing the column dip direction (or strike) and the dip angle of a measured plane…

data(example_planes)
head(example_planes)
#> # A tibble: 6 × 4
#>   dipdir   dip quality feature_type
#>    <dbl> <dbl>   <dbl> <chr>       
#> 1    142    52       3 foliation   
#> 2    135    43       3 foliation   
#> 3    148    42       3 foliation   
#> 4    150    46       3 foliation   
#> 5    139    51       3 foliation   
#> 6    158    51       3 foliation

or the trend (azimuth) and plunge (inclination) of a measured line…

data(example_lines)
head(example_lines)
#> # A tibble: 6 × 4
#>   trend plunge quality feature_type
#>   <dbl>  <dbl>   <dbl> <chr>       
#> 1    54     13       3 stretching  
#> 2    61     15       3 stretching  
#> 3    74     14      NA stretching  
#> 4    80     19      NA stretching  
#> 5    63     17      NA stretching  
#> 6    76     10      NA stretching

To convert these data frames to spherical objects, use the Plane() and Line() functions from the structr package. These functions take the dip direction and dip angle for planes, and the trend and plunge for lines as arguments.

data(example_planes)
planes <- Plane(example_planes$dipdir, example_planes$dip)
lines <- Line(example_lines$trend, example_lines$plunge)

If the raw data was imported using read_strabo_JSON() this step is not necessary as the data will come already in the correct format.

The spherical objects can be easily converted into Cartesian coordinate vectors using the functions line2vec() or plane2vec():

lines_vector <- line2vec(lines)
head(lines_vector)
#>              x         y         z
#> [1,] 0.5727204 0.7882819 0.2249511
#> [2,] 0.4682901 0.8448178 0.2588190
#> [3,] 0.2674497 0.9327081 0.2419219
#> [4,] 0.1641876 0.9311540 0.3255682
#> [5,] 0.4341533 0.8520738 0.2923717
#> [6,] 0.2382466 0.9555548 0.1736482

planes_as_line <- plane2vec(planes)
head(planes_as_line)
#>              x          y         z
#> [1,] 0.6209609 -0.4851479 0.6156615
#> [2,] 0.4822457 -0.4822457 0.7313537
#> [3,] 0.5674549 -0.3545852 0.7431448
#> [4,] 0.6229665 -0.3596699 0.6946584
#> [5,] 0.5865195 -0.5098536 0.6293204
#> [6,] 0.7205572 -0.2911240 0.6293204

which produces the same output as

head(line2vec(planes_as_line))
#>              x           y            z
#> [1,] 0.9999054 0.010837212 -0.008467326
#> [2,] 0.9999292 0.008416377 -0.008416675
#> [3,] 0.9999318 0.009903605 -0.006188640
#> [4,] 0.9999212 0.010872389 -0.006277383
#> [5,] 0.9999080 0.010236112 -0.008898507
#> [6,] 0.9999080 0.012575602 -0.005081050

Some helpers

Converts strike into dip direction using right-hand rule

rhr2dd(271)
#> [1] 1
dd2rhr(1)
#> [1] 271

# parse_strike_dip(c("E30N", "W10S"), c("45NW", "4SE"))

Vector operations

Since the spherical or vector objects are easily convertible, they can be used for all sort of vector operations, such as the magnitude (or length), the angle between vectors, dot product, cross product, projection and rotation.

Define some example vectors:

line1 <- Line(120, 50)
line2 <- Line(10, 30)

The vector length (or magnitude):

vlength(line1)
#> [1] 1

Orientation vectors are by definition unit vectors, i.e. their length is equal to 1.

The angle between two vectors

vangle(line1, line2)
#> [1] 78.89371

The dot product (or scalar product) of two vectors

vdot(line1, line2)
#> [1] 0.1926297

Intuitively, it tells us something about how much two vectors point in the same direction.

The cross product of two vectors:

vcross(line1, line2)
#>       azimuth   plunge
#> [1,] 258.6679 32.21399
#> attr(,"class")
#> [1] "line"

This gives the vector that is perpendicular to the plane spanned by the two vectors.

The projection of a vector on another vector:

vproject(line1, line2)
#>      azimuth plunge
#> [1,]      10     30
#> attr(,"class")
#> [1] "line"

Because of vectors a unit vectors, the projected vector is equal to the second vector.

The rotation of a vector about another vector (rotation axis) by a specified rotation angle:

vrotate(line1, rotaxis = line2, rotangle = 45)
#>       azimuth   plunge
#> [1,] 210.5039 70.01332
#> attr(,"class")
#> [1] "line"

Tobias Stephan

2025-08-08

Import

Data conversion to spherical objects

Some helpers

Vector operations